Physiology of the Swallow
Stages of the Swallow
The oral preparatory phase
This part of the swallow is voluntary. It is a mechanical phase that can be by-passed by dropping liquid or food into the back of the throat.
In this stage, the food is chewed into smaller pieces and tasted. It is also mixed with saliva from three pairs of salivary glands, which are innervated by the glossopharyngeal nerve. The food and saliva form a bolus of material.
The bolus is kept in the front of the mouth, against the hard palate by the tongue. The front of the tongue is elevated with its tip on the alveolar ridge. The back of the tongue is elevated and the soft palate is pulled anteriorly against it to keep the food in the oral cavity (the airway is open and nasal breathing continues during this phase). Labial seal is maintained to prevent food from leaking out of the mouth. Buccal muscles are tense. This prevents pocketing of food. Duration of the oral-preparatory stage is variable (Logemann, 1983,1989, 1997).
The oral transport stage
This stage of the swallow is also voluntary. It starts with the jaws and lips closed, and the tongue tip on the alveolar ridge. The pattern-elicited response is initiated at the end of this stage.
Inspiration is reflexively inhibited at the beginning of this stage. The food is moved to the back of the mouth by the tongue via an anterior to posterior rolling motion. The anterior portion of the tongue is retracted and depressed while the posterior portion is retracted and elevated against the hard palate. When the bolus passes the anterior faucial pillars/touches the posterior wall of the pharynx, the oral stage ends and the pharyngeal stage begins as the tongue driving force or the tongue's plunger action, forces the bolus into the pharynx. Logemann (1997) describes the "pharyngeal tongue" which extends from the velum to the hyoid bone and valleculae. The "oral tongue" which extends from the tip to the back, adjacent to the velum, functions during the oral stage of the swallow while the "pharyngeal tongue" functions during the pharyngeal stage. The oral transport stage lasts one second (Logemann, 1989, 1998; Dobie, 1978).
The pharyngeal stage
(Logemann, 1989, 1997, 1998; Cherney, 1994)
The pharyngeal stage of the swallow is involuntary. It is the most critical stage of the swallow; airway closure must occur to prevent the bolus from entering the respiratory system. A number of things occur almost simultaneously: .
1. Sensory information from receptors in the back of the mouth and in the pharynx goes to the swallowing center in the medulla via CN. IX. The palatopharyngeal folds pull together medially to form a slit in the upper pharynx. The bolus passes through this slit.
2. The velum is raised, primarily by the levator and tensor veli palatini muscles. This prevents the entry of food into the nasopharynx. The narrowing of the upper pharynx due to the contraction of superior pharyngeal constrictor muscle helps to close the velopharyngeal port.
3. The tongue is retracted, preventing the food from re-entering the mouth.
The laryngeal substage
Three actions occur simultaneously to protect the airway. (Obviously, inspiration is inhibited during the pharyngeal stage of the swallow.)
1. The larynx and the hyoid bone are pulled both upward and forward. This movement enlarges the pharynx. It also creates a vacuum in the hypopharynx, pulling the bolus downward. Finally, it contributes to the relaxation of the cricopharyngeous muscle (Dobie, 1978; Logemann, 1983, 1989, 1997)
2. The true and false vocal folds adduct. (Closure begins at the level of the true vocal folds and progresses up to the false vocal folds and then to the ari-epiglottic folds.)
3. The epiglottis drops down over the top of the larynx, protecting the airway and diverting the bolus into the pyriform sinuses. The bolus passes down on both sides of the epiglottis. If the bolus is liquid, the epiglottis acts as a ledge to slow its movement through the pharynx, giving the vocal folds time to adduct and the larynx time to elevate. (Nevertheless, the action of the epiglottis is the least important of these three movements.)
Four factors cause food to move down the pharynx during the rest of the pharyngeal stage (Cherney, et al., 1994; Logemann, 1983, 1989, 1997):
1. The tongue driving force using the "pharyngeal tongue"
2. The stripping action of the pharyngeal constrictors
3. The presence of negative pressure in the laryngopharynx-the laryngeal phase of the pharyngeal stage
4. Gravity
It is believed by some that the tongue driving force (TDF) is the most important of these factors. This generates pressure in the upper pharynx.
The pharyngeal stage ends when the cricopharyngus muscle relaxes, allowing the bolus to enter the esophagus. It is believed that the following three factors affect the opening of the p.e. segment, although the process is not currently well-understood:
1. Innervation by the vagus nerve
2. The timing of the stripping action in the pharynx may somehow trigger the relaxation of the p.e. segment.
3. The elevation of the larynx may pull the muscle upward, causing it to open by stretching it and therefore causing it to relax.
The esophageal stage
In this phase, which is of course involuntary, the bolus is moved down the esophagus via peristaltic wave motion with some help from gravity.
At the beginning of the phase, the larynx lowers, returning to its normal position. The cricopharyngeus muscle contracts to prevent reflux and respiration resumes.
This stage normally lasts between eight and twenty seconds, but in elderly individuals peristalsis is slower (Logemann, 1989, 1997; Dobie, 1978).
Esophageal problems can cause the reflux of food back into the pharynx, leading to aspiration. Speech pathologists do not treat esophageal problems, but should be aware of them, and be able to differentiate them from problems that are within their scope of practice.
*** Note that 90% of the swallow occurs during expiration; an apneal pause between 1 and 3.5 seconds in duration occurs during the oral and pharyngeal stages (Logemann, 1989; 1997).
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Digestion in Human Beings 3D (click here)
Stages of the Swallow The oral preparatory phase
This part of the swallow is voluntary. It is a mechanical phase that can be by-passed by dropping liquid or food into the back of the throat.
In this stage, the food is chewed into smaller pieces and tasted. It is also mixed with saliva from three pairs of salivary glands, which are innervated by the glossopharyngeal nerve. The food and saliva form a bolus of material.
The bolus is kept in the front of the mouth, against the hard palate by the tongue. The front of the tongue is elevated with its tip on the alveolar ridge. The back of the tongue is elevated and the soft palate is pulled anteriorly against it to keep the food in the oral cavity (the airway is open and nasal breathing continues during this phase). Labial seal is maintained to prevent food from leaking out of the mouth. Buccal muscles are tense. This prevents pocketing of food. Duration of the oral-preparatory stage is variable (Logemann, 1983,1989, 1997).
The oral transport stage
This stage of the swallow is also voluntary. It starts with the jaws and lips closed, and the tongue tip on the alveolar ridge. The pattern-elicited response is initiated at the end of this stage.
Inspiration is reflexively inhibited at the beginning of this stage. The food is moved to the back of the mouth by the tongue via an anterior to posterior rolling motion. The anterior portion of the tongue is retracted and depressed while the posterior portion is retracted and elevated against the hard palate. When the bolus passes the anterior faucial pillars/touches the posterior wall of the pharynx, the oral stage ends and the pharyngeal stage begins as the tongue driving force or the tongue's plunger action, forces the bolus into the pharynx. Logemann (1997) describes the "pharyngeal tongue" which extends from the velum to the hyoid bone and valleculae. The "oral tongue" which extends from the tip to the back, adjacent to the velum, functions during the oral stage of the swallow while the "pharyngeal tongue" functions during the pharyngeal stage. The oral transport stage lasts one second (Logemann, 1989, 1998; Dobie, 1978).
The pharyngeal stage
(Logemann, 1989, 1997, 1998; Cherney, 1994)
The pharyngeal stage of the swallow is involuntary. It is the most critical stage of the swallow; airway closure must occur to prevent the bolus from entering the respiratory system. A number of things occur almost simultaneously: .
1. Sensory information from receptors in the back of the mouth and in the pharynx goes to the swallowing center in the medulla via CN. IX. The palatopharyngeal folds pull together medially to form a slit in the upper pharynx. The bolus passes through this slit.
2. The velum is raised, primarily by the levator and tensor veli palatini muscles. This prevents the entry of food into the nasopharynx. The narrowing of the upper pharynx due to the contraction of superior pharyngeal constrictor muscle helps to close the velopharyngeal port.
3. The tongue is retracted, preventing the food from re-entering the mouth.
The laryngeal substage
Three actions occur simultaneously to protect the airway. (Obviously, inspiration is inhibited during the pharyngeal stage of the swallow.)
1. The larynx and the hyoid bone are pulled both upward and forward. This movement enlarges the pharynx. It also creates a vacuum in the hypopharynx, pulling the bolus downward. Finally, it contributes to the relaxation of the cricopharyngeous muscle (Dobie, 1978; Logemann, 1983, 1989, 1997)
2. The true and false vocal folds adduct. (Closure begins at the level of the true vocal folds and progresses up to the false vocal folds and then to the ari-epiglottic folds.)
3. The epiglottis drops down over the top of the larynx, protecting the airway and diverting the bolus into the pyriform sinuses. The bolus passes down on both sides of the epiglottis. If the bolus is liquid, the epiglottis acts as a ledge to slow its movement through the pharynx, giving the vocal folds time to adduct and the larynx time to elevate. (Nevertheless, the action of the epiglottis is the least important of these three movements.)
Four factors cause food to move down the pharynx during the rest of the pharyngeal stage (Cherney, et al., 1994; Logemann, 1983, 1989, 1997):
1. The tongue driving force using the "pharyngeal tongue"
2. The stripping action of the pharyngeal constrictors
3. The presence of negative pressure in the laryngopharynx-the laryngeal phase of the pharyngeal stage
4. Gravity
It is believed by some that the tongue driving force (TDF) is the most important of these factors. This generates pressure in the upper pharynx.
The pharyngeal stage ends when the cricopharyngus muscle relaxes, allowing the bolus to enter the esophagus. It is believed that the following three factors affect the opening of the p.e. segment, although the process is not currently well-understood:
1. Innervation by the vagus nerve
2. The timing of the stripping action in the pharynx may somehow trigger the relaxation of the p.e. segment.
3. The elevation of the larynx may pull the muscle upward, causing it to open by stretching it and therefore causing it to relax.
The esophageal stage
In this phase, which is of course involuntary, the bolus is moved down the esophagus via peristaltic wave motion with some help from gravity.
At the beginning of the phase, the larynx lowers, returning to its normal position. The cricopharyngeus muscle contracts to prevent reflux and respiration resumes.
This stage normally lasts between eight and twenty seconds, but in elderly individuals peristalsis is slower (Logemann, 1989, 1997; Dobie, 1978).
Esophageal problems can cause the reflux of food back into the pharynx, leading to aspiration. Speech pathologists do not treat esophageal problems, but should be aware of them, and be able to differentiate them from problems that are within their scope of practice.
*** Note that 90% of the swallow occurs during expiration; an apneal pause between 1 and 3.5 seconds in duration occurs during the oral and pharyngeal stages (Logemann, 1989; 1997).
Click here for more details Youtube
Digestion in Human Beings 3D (click here)
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